1. Field of the Invention
Embodiments of the present invention relate to a method of forming an electromechanical transducer film, the electromechanical transducer film, an electromechanical transducer element, a liquid discharge head, and an image forming device. Specifically, the embodiments of the present invention relate to an electromechanical transducer element, an electromechanical transducer film included in the electromechanical transducer element, and a method of forming the electromechanical transducer film that are utilized as a piezoelectric element of a liquid discharge head included in an inkjet recording device; a printing machine, such as a printer, a facsimile machine, a copier, a plotter, and a screen printing machine; or a combined machine having the functions of these devices.
2. Description of the Related Art
In an inkjet recording device which is utilized as an image recording device, such as a printer, a facsimile machine, or a copier; or as an image forming device, an image is formed by discharging ink droplets from a recording head onto an object, such as a sheet, which is utilized as a recording medium. The recording head includes a nozzle for discharging ink droplets; a pressurizing chamber that communicates with the nozzle (also referred to as an ink flow channel, a pressurized liquid chamber, a pressure chamber, a discharge chamber, or a liquid chamber); and an electromechanical transducer element (e.g., a piezoelectric element) that applies pressure to the ink in the pressurizing chamber, an electro-thermal conversion element (e.g., a heater), or an energy generating unit formed of an oscillation plate forming a wall surface of the ink flow channel and an electrode facing the oscillation plate. In the recording head, the ink in the pressurizing chamber is pressed by energy generated by the energy generating unit or the like, thereby discharging the ink droplets from the nozzle (cf. Patent Document 1 (Japanese Unexamined Published Application No. H04-168277), Patent Document 2 (Japanese Unexamined Published Application No. 2003-297825), and Patent Document 3 (Japanese Registered Patent No. 4432776)). Patent Document 3 discloses a configuration of a recording head including a piezoelectric element in which a lower electrode disposed on a substrate (a first electrode); an electromechanical transducer layer; and an upper electrode (a second electrode) are laminated.
In general, in the recording head, independent piezoelectric elements for generating the pressure for causing the corresponding pressurizing chambers to discharge the ink are arranged. The piezoelectric elements are referred to as electromechanical transducer elements. The electromechanical transducer element converts an electrical input into a mechanical deformation. The electromechanical transducer element has a laminated structure such that a film of a piezoelectric material is sandwiched between an upper electrode and a lower electrode for inputting an electric signal. As the piezoelectric material, ceramics of lead zirconate titanate (hereinafter, abbreviated as “PZT”) and the like are utilized. Since the main components of these materials are plural metal oxides, these materials are usually referred to as metal composite oxides.
(Conventional Method of Forming Individual Piezoelectric Element)
A piezoelectric film is formed on a lower electrode by a known film formation method, such as various vacuum deposition methods (e.g., the sputtering method, the MO-CVD method (e.g., a chemical vapor deposition using a metal organic compound), the vacuum evaporation method, and the ion plating method), the sol-gel method, the hydrothermal synthesis method, the aerosol deposition method (abbreviated as “AD method”), and the metal organic deposition (MOD). Subsequently, after the upper electrode is formed, patterning by photography and etching is performed on the upper electrode. Similarly, patterning is performed on the piezoelectric film and the lower electrode, and thereby independent piezoelectric elements are formed.
The dry etching is not easily applied to a metal composite oxide, especially to the PZT. A Si semiconductor device can be easily etching-processed by the reactive ion etching (abbreviated as “RIE”). However, for such a material, a special RIE, in which ICP plasma, ECR plasma, and helicon plasma are used together, is performed to increase plasma energy of ionic species. Such a method results in a higher cost. Further, it is difficult to improve the selectivity between such a material and the lower electrode film. Especially, for a substrate having a large surface area, nonuniformity in the etching rate can be a major obstacle for forming a film. The above manufacturing process can be omitted, if desired portions are coated with the PZT films in advance, since the PZT films are difficult to be etched. However, such an attempt has not been made, with a few exceptions.
Incidentally, Non-Patent Document 1 (K. D. Budd, S. K. Dey, D. A. Payne, Proc. Brit. Ceram. Soc. 36, 107 (1985)) discloses a technique for forming a thin film of a metal composite oxide by the sol-gel method. Further, Non-Patent Document 2 (A. Kumar and G. M. Whitesides, Appl. Phys. Lett., 63, 2002 (1993)) discloses that a film of alkanethiol can be formed on a film of Au as a Self Assembled Monolayer (SAM). Additionally, Non-Patent Document 2 discloses that a SAM pattern can be copied using the micro-contact printing method which utilizes the above phenomenon, and the SAM pattern can be utilized for a subsequent process, such as the etching process.
(Conventional Example of Forming Separated PZT Films)
Conventional methods of forming separated PZT films include the hydrothermal method, the vacuum deposition method, the AD method, and the inkjet method. It has been known that, in the inkjet method, a PZT precursor solution (sol-gel solution) can be applied by discharging the liquid droplets at high resolution.
In the inkjet method, higher resolution may be required, as a desired pattern becomes finer. Here, the pattern is formed by applying the sol-gel solution, which has become like an ink by the inkjet method, to a surface of a metal on which a first electrode is formed. In order to form a high-resolution pattern, sizes of the sol-gel solution droplets discharged from the nozzle of the inkjet head are reduced. However, when the sizes of the sol-gel solution droplets are reduced, the weight of each of the sol-gel solution droplets is reduced. Therefore, it becomes difficult to control the positions where the sol-gel solution droplets are adhered to, and it becomes difficult to form a desired pattern. Further, as the sizes of the sol-gel solution droplets are reduced, mist of the sol-gel solution tends to be generated from the nozzle of the inkjet head. Since sizes of droplets included in the mist are smaller than those of the sol-gel solution droplets (the dot diameter of each of the droplets of the mist is less than or equal to a quarter of the dot diameter of the sol-gel solution droplet), the droplets of the mist tend to be scattered in various directions from the vicinity of the nozzle surface. Hence, the sol-gel solution may be adhered to outside an area of a desired pattern. Therefore, many defects may be formed on the surface of the metal that forms the first electrode, and consequently stability becomes insufficient as an electromechanical transducer element.
On the other hand, even if the sol-gel solution droplets, whose sizes have been reduced, are adhered to inside the area of the desired pattern, since the amount of the solution is small, it is difficult to ensure a large area, which includes the position where the sol-gel solution droplet has been adhered to, for leveling the sol-gel solution on the surface of the metal that forms the first electrode, even though the surface of the metal is highly hydrophilic. Therefore, the sol-gel solution does not spread to edges of the desired pattern. Further, if it takes a relatively long time for drying the sol-gel droplets after they have been adhered to the surface, the dots of the neighboring sol-gel solution droplets, which have been adhered to the surface of the metal forming the first electrode, clump together and are locally integrated in the desired pattern to be formed. When the electromechanical transducer film is formed by applying the drying process, the thermal decomposition process, and the crystallization process to the sol-gel solution in this condition, the area of the formed electromechanical transducer film may be narrower than the area of the desired pattern. Furthermore, since the film thickness on the surface may become uneven, cracks tend to occur. In addition, because of the unevenness of the generated film, the electrical characteristic of the electromechanical element formed of the film may be insufficient.